In a general way quick filters (Strainer) which are automatic are equipped with mechanical systems which are motorized to ensure their cleaning. These mechanical systems necessitate plurimetallic constructions which form corrosive electrolytic couples. On the other hand the frictions in dirty water containing very often sand cause a very rapid wearing off of the apparatus.
Finally, these "strainers" are always cleaned by means of a counter current (Back-Wash) which is a drawback particularly when there are fibers creating a mat or interlace within the filtrating elements.
Swiss patents 516 331, 532 409 and 597 894 have presented an automatic filter having none of these three drawbacks, no complicated mechanics, no "Back-wash." The use of this system has demonstrated its security and riability.
These filters which constitute an important technical progress over the preceeding filters have nevertheless certain drawbacks which are the following:
a) Each filtering element has to be equipped with a cleaning valve. To obtain a non-stop filtration it is necessary to have multi-element filters therefore equipped with several valves. The more elements there are, therefore valves, the more the influence of the cleaning of the filtrated outflow is low, but the more the filter is expensive for its construction and installation. PA1 b) The tubular envelop requires an elaborated construction in a qualified workshop and uses high quality materials, in principal stainless steels, which leads to a high manufacturing cost of the filter.